The Earth is undergoing a sixth mass extinction, with scientists warning that the “biological annihilation” of wildlife is “more severe than perceived”.

Blaming the overpopulation and over-consumption of humans, the researchers said the world had a window of about 20-30 years at most to tackle the crisis.

“Earth is experiencing a huge episode of population declines and extirpations” – when a species is wiped out in a particular location – “which will have negative cascading consequences on ecosystem functioning and services vital to sustaining civilisation,” the researchers wrote in the journal Proceedings of the National Academy of Sciences.

“We describe this as a ‘biological annihilation’ to highlight the current magnitude of Earth’s ongoing sixth major extinction event.”

In the study, researchers from Stanford University and the National Autonomous University of Mexico examined the population trends of 27,600 vertebrate species such as birds, amphibians, mammals, and reptiles, including a detailed analysis of 177 species of mammals.

In 2016, there were only 7,000 cheetahs left on the planet CREDIT: PA

They found that as much as 50% of the number of individuals animals that once shared Earth with us have already disappeared and billions of populations of animals are gone.

The detailed study of 117 species found most of them have lost more than 40% of their geographic ranges over the years, and almost half have lost more than 80% of their ranges in the period between 1900–2015.

Among the species in danger were cheetahs, with only 7,000 left alive in 2016. There were fewer than 5,000 Borneo and Sumatran orangutans and populations of the African lion dropped 43% since 1993.

” We emphasise that the sixth mass extinction is already here and the window for effective action is very short, probably two or three decades at most,” the scientists wrote.

The main factors behind these losses are human overpopulation and continued population growth, and overconsumption, especially by the rich.

This swift decline in wildlife has “is already damaging the services ecosystems provide to civilisation”, the study found.

“The serious warning in our paper needs to be heeded because civilisation depends utterly on the plants, animals, and microorganisms of Earth that supply it with essential ecosystem services ranging from crop pollination and protection to supplying food from the sea and maintaining a livable climate,” Prof Paul Ehrlich, one of the scientists involved in the study, told the Guardian.

The scientists conclude: “The resulting biological annihilation obviously will have serious ecological, economic and social consequences. Humanity will eventually pay a very high price for the decimation of the only assemblage of life that we know of in the universe.”

“All signs point to ever more powerful assaults on biodiversity in the next two decades, painting a dismal picture of the future of life, including human life,” they wrote.

While the world has seen five extinctions in its history, the current one is unfolding much quicker.

Noting that the Earth had lost 200 species of vertebrates in the past 100 years alone, the researchers said that if it had followed the trends of the past two million years, those losses should have taken place over 10,000 years.

Elizabeth Kolbert, author of “The Sixth Extinction”, said humans were leaving the world “a much, much poorer place”.

“An extinction should be something that’s very unusual,” Ms Kolbert told CBS News. “When you can identify lots of species that have gone extinct or are on the verge of extinction, that’s actually a very unusual time in the Earth’s history and a very dangerous one.”